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NEGBETTI AND ZAMHRA, HOLBORN YIADUCT, E.C., 



FIG. 121. FIG. 122. FIG. 123. FIG. 124. 



163. Singer's Electrometer for Atmospherical Electricity. 



(fig. 120). This instrument is arranged with a brass rod about two feet in length 

 and a clip for the reception of a lighted cigar fusee ; the electricity is collected 

 by the flame, and cond acted down the rod to a pair of gold leaves, which 

 separate according to the amount ; the kind is determined by the effect of 

 either a stick of excited sealing-wax, or a glass rod, supplied with the instrument 



A glass rod when rubbed produces positive electricity ; a stick of sealing- 

 wax similarly treated produces negative ; if, therefore, when the leaves are sepa- 

 rate, we apply an excited glass rod, and they separate still further, the electricity 

 is positive ; if they approach it is negative ; on the contrary, if we use a stick of 

 sealing-wax, the leaves will separate if they are charged with negative electricity, 

 and converge if positively charged, from the fact that all bodies similarly 

 electrified repel each other, whilst those oppositely electrified attract each other. 



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A book containing strips of gold leaf, to replace the gold leaves when torn 

 or broken in use. Price 016 



To mount fresh gold leaves, unscrew and withdraw the brass plate to 

 which is attached the rod supporting the leaves : then moisten with the breath 

 the flat piece of brass, and press it gently down on one strip of gold, whilst 

 the book is only partly opened ; the second leaf is attached in the same manner. 



164. Bohnenberger's Electroscope (fig. 121), with Zamboni's Dry 

 Piles, arranged with adjustments for regulating the distance between the gold 

 leaf and the polar plates, an exceedingly delicate instrument for indicating the 

 presence and quality of electrical currents. 



It can be mounted with a metallic conductor, and used with great advan- 

 tage for observing atmospheric electricity. The principal parts of the instrument, 

 as improved by Becquerel, are the following:^ I?, fig. 96, is a small 



